Traditionally, stored program controlled communication switching systems have included a single processing entity to control system switching in response to a program stored in memory. As technology and system design evolved, it was found desirable to separate certain routine functions from the main processing entity to save its processing time for more complex system functions and decisions. Today, systems are being designed which also distribute some of the more complex system functions and decisions among several intelligent processors.
The advantages of distributed control in communication switching systems must not be achieved at the expense of system reliability. It is essential, for example, that the integrity of the communication links between processors be maintained despite the failure of a particular system component. The high reliability goals typically set for communication switching systems are frequently met by implementing those systems with redundant hardware. For example, redundant switching networks can be in place wherein an active network handles all traffic until it is determined that it has failed. A standby network then becomes active and handles traffic while the failure is diagnosed and corrective measures are taken. However, in some known distributed control switching systems part of the same switching network used to interconnect subscribers is used to convey control information between processors. Even if redundant switching networks were included in the implementation of such systems, a loss of communication between processors caused by the failure of the active switching network would make system recovery unnecessarily complex and time consuming. The present invention is a distributed control switching system having both active and standby switching networks wherein control links between processors can selectively be maintained through both switching networks such that a control link through the standby network can advantageously be used to achieve rapid system recovery after the failure of the active network.